Method for preparing copper foil with insulating layer and cooper foil with insulating layer prepared by the method, and printed wiring board using the cooper foil with insulating layer

ABSTRACT

To provide a method of manufacturing a material which can make a skeletal component as thin as possible to be contained in an insulating layer in a manufactured copper clad laminate and can securely prevent the direct contact between the nodular treatment surface of the attached copper foil and a skeletal component. In order to attain the object, here is adopted “a method of manufacturing a copper foil with an insulating layer  1  which method is a method of manufacturing a copper foil provided with a semi-cured insulating resin layer containing a skeletal component on one side surface of the copper foil, and is characterized in that: a first thermosetting resin layer  3  in an uncured or semi-cured state is provided on one side surface of a copper foil  2 ; a nonwoven fabric  5  or a woven cloth  5  to be a skeletal component is press-bonded onto a first thermosetting resin layer  3 ; a second thermosetting resin layer  7  is formed on a surface of a press-bonded nonwoven fabric  5  or woven cloth  5 ; and a semi-cured insulating layer containing the nonwoven fabric  5  or the woven cloth  5  is formed on one side surface of the copper foil  2  by drying into a semi-cured state.”

TECHNICAL FIELD

[0001] The present invention relates to a method of manufacturing acopper foil with an insulating layer, a copper foil with an insulatinglayer obtained with the manufacturing method, and a multilayer printedcircuit board using the copper foil with an insulating layer.

BACKGROUND ART

[0002] As for recent multilayer printed circuit boards, downsizing ofthe via holes has been rapidly promoted in parallel with the circuitminiaturization required to multilayer printed circuit boards. In thisconnection, the conventional mechanical drilling machining has becomedifficult to be applied to such microfabrication, and alternatively thelaser drilling machining has been generally prevailing in suchmicrofabrication.

[0003] As the laser drilling machining has come into wide use, themultilayer printed circuit boards manufactured by use of theconventional glass-epoxy base material of FR-4 prepreg have proved to bepoor in laser drilling workability. It is the glass cloth incorporatedas skeletal component in glass-epoxy base material that has been firstrecognized as problematic. Glass cloth is a woven stuff and glass itselfis poor in laser machining workability, and hence drilling withsatisfactory precision has been impossible with glass cloth.

[0004] Thus, the present inventors have been supplying to the market thecopper foil with resin in which exclusively a semi-cured resin layerwithout incorporating a skeletal component is provided on the surface ofthe copper foil. Accordingly, it has been made possible to manufacture,with applying the built-up processing method but without using prepreg,the copper clad laminates which are excellent in the laser drillingworkability, this situation having made it possible to supply highquality multilayer printed circuit boards. In other words, the copperfoil with resin has the characteristics that it is light in weight andexcellent in the laser drilling workability owing to the absence of theskeletal component therein, and simultaneously, the copper foil withresin has the following drawbacks owing to the absence of the skeletalcomponent therein.

[0005] Namely, there has been a problem that a copper clad laminatemanufactured only with the copper foil with resin is insufficient in themechanical strength of the resin layer thereof against such externalforces as bending, tensile, and impact forces. The copper foil withresin has no reinforcing material, and thus the quality control isdifficult for a copper clad laminate manufactured only with the copperfoil with resin, since the thickness of an insulating layer within alaminate layer varies extremely widely in a system having nonuniformcopper circuit densities in the inner layer circuits. The copper foilwith resin is a material large in thermal expansion coefficient, andthus tends to generate a stress in the interface with a different typeof material, for example, with a copper circuit, resulting in adverseeffects to the board reliability. Among other drawbacks pointed out,there is a drawback that a copper clad laminate manufactured only withthe copper foil with resin is low in strength so that pads sink into thelaminate during wire bonding of IC chips, resulting in failure inobtaining stable bonding.

[0006] On the other hand, in the field of prepreg, there have also beensupplied products in which the skeletal component is devised so that thelaser drilling workability is improved while retaining the abovedescribed mechanical strength. To be more specific, it has been saidthat when glass cloth is used as the skeletal component, the laserdrilling workability is generally degraded; accordingly, it has becomegeneral to use the nonwoven glass fabric as the skeletal componentinstead of the woven glass cloth. The use of nonwoven fabric hasimproved the nonuniformity in cloth thread as seen when the nonwovenfabric is used as the skeletal component, thereby significantlyimproving the laser drilling workability.

[0007] However, as for the prepreg containing a skeletal component,there is usually adopted a method in which the skeletal component isimpregnated with a resin component, and then dried, which methodaccordingly causes problems.

[0008] To be more specific, the nonwoven fabric itself is inferior instrength to the woven glass cloth, and accordingly, there has been adrawback that when the impregnated unwoven fabric is taken out of theimpregnating resin, sometimes the impregnated nonwoven fabric tends tobreak adversely owing to the weight of the resin impregnating thereinto.Even with the woven glass cloth, a similar drawback has tended to occurwith decreasing cloth thickness. Thus, although it is desirable to useeither a thinner nonwoven fabric or a thinner woven cloth, actuallythere has been a restriction in reducing the thickness of a nowovenfabric or a woven cloth, in consideration of the strength required tothe insulating layers incorporated into a fabricated copper cladlaminate.

[0009] Thus, there has been attempted to supply those prepregs which useeither thinner nonwoven fabric or woven cloth, through achieving theobject that the insulating resin layer is reduced in thickness for thepurpose of weight reduction, and simultaneously reducing the resincontent impregnated into the nowoven fabric or the woven cloth. A copperclad laminate is manufactured by press working to make a copper foiladhere onto the surface of a prepreg. In this case, the copper foil hasbeen beforehand subjected to the nodular treatment to form concavitiesand convexities on the surface thereof, so that the nodular treatmentsurface of the copper foil go into the resin portion in the basematerial to increase the adhesion strength through obtaining theanchoring effect; when the impregnated resin amount is made to be equalto or lower than a certain level, the skeletal component and the nodulartreatment surface of the copper foil come into contact with each other,resulting in degraded adhesion of the base material resin and therebyresulting in the degraded peel strength of the laminate; and inaddition, it has become anticipated that the direct contact between theskeletal component and the copper foil possibly facilitates themigration of the copper foil along the skeletal component fibers.

[0010] From the above, there have been desired a material and a methodwhich material and method make it possible to prevent more securely thecontact between the nodular treatment surface of the attached copperfoil and the skeletal component, through raising the resin content ratioin an insulating resin layer by making the skeletal componentincorporated into the insulating resin layer of a fabricated copper cladlaminate as thin as possible.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 shows a schematic view of the copper foil with aninsulating layer obtained by the manufacturing method related to thepresent invention.

[0012]FIGS. 2 and 3 each shows a schematic view of a production flow ofa copper foil with an insulating layer.

[0013]FIG. 4 shows the lamination concept and schematic sectional viewsof a multilayer copper clad laminate for use in evaluation. FIG. 5 showsschematically a production flow of an insulating resin board for use inevaluation, and the schematic sectional views of the insulating resinboard.

SUMMARY OF THE INVENTION

[0014] According to the judgment of the present inventors, as a resultof diligent study, as far as the conventional method of manufacturingprepreg is adopted, the skeletal component which can be used with thatmethod cannot be as thin as 120 μm or below for a nonwoven fabric andcannot be as thin as 20 μm or below for a woven cloth; and the availablethickness limit as measured for the prepreg impregnated with resin is ofthe order of 120 μm for a nonwoven fabric and of the order of 30 μm fora woven cloth. Thus, the present inventors have reached an idea thatwhen an insulating resin layer incorporating a skeletal componenttherein is directly formed on the surface of a copper foil by using themethod to be described below, the thickness of the nonwoven fabric orthe woven cloth to be used can be reduced, and the total thickness ofthe insulating layer as a result of a combination of the skeletalcomponent and the resin can be arbitrarily controlled, and in addition,the contact between the nodular treatment surface of the copper foil andthe nonwoven fabric or the woven cloth can be securely prevented.

[0015] Among the woven skeletal components, some recently developedcomponents are excellent in laser drilling workability. In other words,strands are each opened in a plane shape, and the sectional shapes ofthe warp strands and weft strands of a woven cloth are flattened, sothat the laser drilling workability of the woven cloth which has beeninferior in the laser drilling workability as compared with the nonwovenfabric in the past, is used for SP cloth which has the same level as thenonwoven fabric. When such an SP cloth is available, it becomesadvantageous to use a woven cloth excellent in the mechanical strengthssuch as the cracking resistance as compared to the use of a nonwovenfabric. Thus, if such a woven cloth can be applied to the insulatinglayer in the copper foil with an insulating layer related to the presentinvention described below, the mechanical strength of the copper foilwith such an insulating layer which is easier to use than the prepreg issignificantly improved. Incidentally, it is preferable to treat with asilane coupling agent the fibers which constitute either the woven clothor the nonwoven fabric, both used in the present invention, in order toimprove the wetting property of the surfaces thereof to the resin. Inthis case, as the silane coupling agent, the amino based silane couplingagent, the epoxy based coupling agent, or the like can be used,according to the purpose.

[0016] The invention set forth in the claims is a method ofmanufacturing a copper foil provided with an insulating semi-cured resinlayer on one side surface thereof which resin layer contains a skeletalcomponent, which method is a method of manufacturing a copper foil withan insulating layer and is characterized in that a semi-cured insulatingresin layer containing a nonwoven fabric or a woven cloth is formed onone side surface of the copper foil by providing the first semi-curedthermosetting resin layer on one side surface of the copper foil, andpress-bonding a skeletal component of either a nowoven fabric or a wovencloth on the first thermosetting resin layer, and then forming thesecond thermosetting resin layer on the surface of the press-bondednonwoven fabric or woven cloth and drying in a semi-cured state. FIG. 1shows a schematic sectional view of the copper foil with an insulatinglayer.

[0017] Now, the manufacturing method is described with reference to FIG.2 where the process flow is illustrated. At the beginning, as FIG. 2(1)shows, on the one side surface of a copper foil 2 is provided the firstsemi-cured thermosetting resin layer 3. The copper foil 2 as referred tohere may be a copper foil for use as electronic material in printedcircuit boards, such as a rolled copper foil obtained by rolling and anelectrodeposited copper foil obtained by electrolysis, that is, the foilmanufacturing method is not specified to any particular one. The copperfoil 2 of the present specification conceptually includes a copper foilwith a carrier foil. A copper foil with a carrier foil has the carrierfoil on the surface of the copper foil reverse to the surface thereofbonded to a base material, and is processed with press working to beused as a copper clad laminate, and subsequently the pressed copper cladlaminate is deprived of the carrier foil to be used as a usual copperclad laminate. The use of a copper foil with a carrier foil has anadvantage that the possible attachment of foreign matters on the surfaceof the copper foil and the possible surface staining during the pressworking can be prevented, and the surface of the copper foil can beprotected against deterioration due to such damages as scratches untiljust before the etching process.

[0018] Generally the epoxy resin is used for the resin constituting thefirst thermosetting resin layer 3, since it is widely used for use inprinted wiring boards. In other words, as for the resin constituting thefirst thermosetting resin layer, there is no particular limitationexcept that the resin is provided with thermosetting property and can beused for printed circuit boards in the electric and electronic materialfields. The first thermosetting resin layer 3 is formed on the surfaceof a copper foil by a method in which a liquid resin material preparedby use of a solvent is applied onto the surface of the copper foil, by amethod in which the resin film in a semi-cured, state is attached to belaminated onto the surface of the copper foil, or by the like. When aliquid resin material is used, there are blended, for example, epoxyresin, a curing agent, and a curing accelerator, and the viscosity isadjusted for application by using a solvent such as methyl ethyl ketone.

[0019] The first thermosetting resin layer 3 formed on the surface ofthe copper foil is maintained in a semi-cured state, in order to therebymake a satisfactory press-bonding of a nonwoven fabric 5 or a wovencloth 5, and to promote a certain amount of resin impregnation into theunwoven fabric or the woven cloth. Accordingly, when a liquid resinmaterial is applied onto the surface of the copper foil 2, and then theresin layer is transformed into a semi-cured state, it is necessary toadjust the dryness level and curing degree by using a hot air dryingdevice, and the like.

[0020] The thickness of the first thermosetting resin layer 3 formed onthe surface of the copper foil 2 is determined in consideration of thethickness of the nonwoven fabric 5 or the woven cloth 5 to be describedbelow. In other words, the thickness of the first thermosetting resinlayer 3 should be equal to or smaller than that of the unwoven fabric 5or that of the woven cloth 5. When the thickness of the firstthermosetting resin layer 3 is made to be larger than that of theunwoven fabric 5 or that of the woven cloth 5, the resin constitutingthe first thermosetting resin layer 3 tends to flow out to pollute theprocessing device during press-bonding of the unwoven fabric 5 or thewoven cloth 5; in particular, when the press roll 6 is polluted, thepolluting matter is transferred onto the surface of the copper foil 2being processed, resulting in product quality degradation.

[0021] On the other hand, the lowest limit for the thickness of thefirst thermosetting resin layer 3 can be determined on the basis of thefollowing consideration. The first thermosetting resin layer 3 is formedon the roughened surface 4 of the copper foil 2 having concavities andconvexities, and hence it is necessary for the thickness of the firstthermosetting resin layer 3 to have at least a certain value sufficientto completely cover over these concavities and convexities. When theseconcavities and convexities of the roughened surface 4 cannot becompletely covered over, these concavities and convexities of theroughened surface 4 of the copper foil 2 come into direct contact withthe nonwoven fabric 5 or the woven cloth 5, failing to achieve theobject of the present invention.

[0022] Thus, in consideration of fact that the thickness of a copperfoil used as an inner layer circuit and subjected to the laser drillingmachining is generally 18 μm or below, research has been made repeatedlyon the basis of the condition that the 10 point average roughness (Rz)of the roughened surface of a copper foil of 18 μm in nominal thicknessis 4.0 μm or below. As a result, the following estimation has been ableto be obtained: by use of either the resin amount to form a resin layerof 3.0 μm in thickness when applied onto a smooth surface or a resinfilm of 3.0 μm or above in thickness, the roughened surface of a copperfoil of 18 μm or below in nominal thickness can be securely coveredover, and such an amount of resin can be left between the roughenedsurface of the copper foil and the nonwoven fabric or the woven cloththat can circumvent the direct contact of the concavities andconvexities of the roughed surface with the nonwoven fabric or the wovencloth, even taking account of the impregnation amount of the resinfluidized again when the nonwoven fabric or the woven cloth ispress-bonded, and moreover even when press working is made. From theabove, it is preferable that the first thermosetting resin layer is 3 μmor above in thickness as converted to the value for the flat plane, andin addition thinner than the nonwoven fabric used as a skeletalcomponent of 50 μm or below in thickness or the woven cloth used as askeletal component of 20 μm or below. Here, the thickness of 3.0 μmconverted to the value for the flat plane means the value of 3.0 μmobtained when a certain amount of resin is applied onto a smooth surfacewithout concavities and convexities; this refers to a concept generallyapplied when an application amount onto a surface with concavities andconvexities is determined.

[0023] When the first thermosetting resin layer 3 is formed on thesurface of the copper foil 2 as described above, then the nonwovenfabric 5 or the woven cloth 5 is attached to the first thermosettingresin layer 3 by use of the press roll 6 as shown in FIG. 2(3). Thenonwoven fabric 5 or the woven cloth 5 becomes the skeletal component,and are used to overcome the poor mechanical strength of theconventional copper foils with resin. The nonwoven fabric 5 or the wovencloth 5 is attached on the thermosetting resin layer 3 by applying aload with the press roll. When the nonwoven fabric 5 or the woven cloth5 is attached on the first thermosetting resin layer 3 in a semi-curedstate, it is necessary to attach the nonwoven fabric 5 or the wovencloth 5 by using a press roll equipped with a heating device, whileheating the roll itself and applying a load of pressure higher than acertain level. This is because the resin in a semi-cured state isfluidized again, and a certain amount of the resin fluidized again isimpregnated into the nonwoven fabric or the woven cloth.

[0024] It is preferable to use the nonwoven fabric or the woven clothmade of any of a glass fiber, an aramid fiber, and a wholly aromaticpolyester fiber having a melting point of 300° C. or above (hereinafter,simply referred to as “a wholly aromatic polyester fiber”), as thenonwoven fabric 5 or the woven cloth 5 used here. Because, both glassfiber and aramid fiber have been used actually for long years for theprinted circuit boards and are thus highly reliable materials. Thewholly aromatic polyester fiber having a melting point of 300° C. orabove is a fiber made of a resin referred to as a liquid crystalpolymer, and the liquid crystal polymer has as the main component apolymer made of 2-hydroxy-6-naphthoic acid and p-hydroxybenzoic acidboth represented by the formula (1). The wholly aromatic polyester fiberhas a low dielectric constant and a low dielectric dissipation factor,and accordingly displays excellent performance as a material forcomposing an electrically insulating layer, so that the wholly aromaticpolyester fiber can be used similarly to the glass fiber and aramidfiber. However, it is not necessary to particularly limit the materialof the nonwoven fabric or the woven cloth, but any material isacceptable which can be used for printed circuit boards and hassufficient mechanical characteristics.

[0025] There is no particular limitation for the thickness of thenonwoven fabric 5 or the woven cloth 5, but as described for the objectof the present invention, it becomes possible to use the thin nonwovenfabric or the thin woven cloth of 50 μm or below in thickness which hasnot been able to be used heretofore. According to the conventionalmethod in which a nonwoven fabric or a woven cloth is dipped into aresin material to impregnate the resin material into the nonwoven fabricor the woven cloth, taken out of the resin material, and dried into asemi-cured state to form a prepreg, a thin nonwoven fabric of 50 μm orbelow in thickness or a thin woven fabric of 20 μm or below in thicknesstends to be easily broken or damaged owing to being weak in mechanicalstrength; even if the break or the damage does not occur, the nonwovenfabric or the woven cloth is pulled by the tension along the lengthwisedirection to be elongated, and as a result there occurs a largedifference between the longitudinal and the transverse expansion andcontraction coefficients of the manufactured prepreg, which results in asignificant deficiency in the dimensional stability as considered to beimportant in what is called, a precise printed circuit boards.

[0026] On the other hand, when the method of manufacturing a copper foilwith an insulating layer 1 related to the present invention is adopted,no break or no damage occurs even with a nonwoven fabric as thin as 50μm or below or with a woven cloth as thin as 20 μm or below. Accordingto the current level of the technique for manufacturing nonwoven fabricsor woven cloths, the minimum thickness limit available within thesufficient guarantee of quality is said to be 45 μm for a nonwovenfabric and 20 μm for a woven cloth. In the future a further thinnernonwoven fabric or woven cloth can be expected to be manufactured.However, generally even when a heavy part such as a flyback transformerof a television set is mounted directly on a printed circuit board, thebending strength of 200 MPa of the board, as assumed to be an insulatingresin board to be described in an embodiment, is said to be sufficientto wear under the usual usage conditions, so that it is contemplatedthat the thickness of a nonwoven fabric or a woven cloth may be properlyselected to be able to clear the above described strength.

[0027] When the attachment of the nonwoven fabric or the woven cloth iscompleted as described above, then a resin constituting the secondthermosetting resin layer 7 is applied onto the nonwoven fabric or thewoven cloth, as FIG. 2(4) shows, to form the second thermosetting resinlayer 7; similarly to the case of the first thermosetting resin layer 3,the epoxy resin is generally used. However, as for the resin forconstituting the second thermosetting resin layer 7, there is no need toset a particular limitation except that it is a resin which is providedwith thermosetting property and can be used for the printed circuitboard in the electric and electronic material fields, similarly to thecase of the first thermosetting resin layer 3. As the method for formingthe second thermosetting resin layer 7, the method for forming the firstthermosetting resin layer 3 can be similarly applied.

[0028] The second thermosetting resin layer 7 formed on the surface ofthe copper foil should be maintained in a semi-cured state. This isbecause the copper foil with an insulating layer is laminated incombination with another printed circuit board material, andpress-molded to be used as a component constituting a printed circuitboard.

[0029] The thickness of the second thermosetting resin layer 7 isdetermined as described below in consideration of the thickness of thenonwoven fabric 5 or the woven cloth 5. Namely, since as describedabove, the thickness of the first thermosetting resin layer 3 is equalto or less than the thickness of the nonwoven fabric 5 or the wovencloth 5, there is a high possibility that the resin constituting thefirst thermosetting resin layer 3 alone is insufficient to yield a statewherein the resin constituting the first thermosetting resin layer 3completely coats the nonwoven fabric or the woven cloth, even when thefirst thermosetting resin layer 3 is press-bonded to the nonwoven fabric5 or the woven cloth 5 to fluidize the resin constituting the firstthermosetting resin layer 3. Accordingly, the second thermosetting resinlayer 7 should be formed with the thickness capable of completelycoating at least the surface of the nonwoven fabric 5 or the woven cloth5.

[0030] Moreover, the thickness of the second thermosetting resin layer 7should be a certain value which can prevent the direct contact of theconcavities and convexities of the roughened surface of the copper foilwith the nonwoven fabric or the woven cloth when the copper foil 2 isattached by the press molding to the second thermosetting resin layer 7.Namely, on the basis of the same idea as applied to the firstthermosetting resin layer 3, it can be assessed that the thickness ofthe second thermosetting resin layer 7 needs to be 5.0 μm or above. Thethickness of the second thermosetting resin layer, as referred to here,means that the thickness converted to the value on the flat surface is5.0 μm or above, similarly to the case of the first thermosetting resinlayer.

[0031] As another method for obtaining a product similar to the copperfoil with an insulating layer obtained with the above describedmanufacturing method, here is a method set forth in a claim as follows:a method of manufacturing a copper foil provided with, on one sidesurface of the copper foil, a semi-cured insulating layer containing asa skeletal component a nonwoven fabric or a woven cloth; and the methodof manufacturing a copper foil with an insulating layer is characterizedin that a semi-cured insulating layer containing a nonwoven fabric or awoven cloth is formed on one side surface of the copper foil as follows:a liquid thermosetting resin layer is provided on one side surface ofthe copper foil, on which layer a nonwoven fabric or a woven cloth issuperposed as a skeletal component; the resin constituting thethermosetting resin layer is made to impregnate into the nonwoven fabricor the woven cloth so as to exude from the opposite side so that thenonwoven fabric or the woven cloth is coated with the resin constitutingthe thermosetting resin layer, and the impregnated woven fabric or theimpregnated woven cloth is dried into a semi-cured state.

[0032] The above manufacturing method is conceptually illustrated inFIG. 3 as a flow of production. On one side surface of a copper foil 2shown in FIG. 3(1), a liquid thermosetting resin layer 3′ is provided asshown in FIG. 3(2), a nonwoven fabric 5 or a woven cloth 5 is superposedon the surface of the thermosetting resin layer 3′, the resin componentconstituting the thermosetting resin layer 3′ is impregnated into thenonwoven fabric 5 or the woven cloth 5 under favor of the capillaryphenomenon exhibited by any fiber of the glass fiber, the aramid fiber,and the wholly aromatic polyester fiber constituting the nonwoven fabric5 or the woven cloth 5 so as to exude from the side surface of thenonwoven fabric 5 or the woven cloth 5 reverse to the surface thereof incontact with the thermosetting resin layer 3′, and thus the surface ofthe nonwoven fabric 5 or the woven cloth 5 is completely coated with theresin to yield a copper foil with an insulating layer as shown in FIG.3(4).

[0033] In the process shown in FIG. 3(3), it is preferable to coat thenonwoven fabric 5 or the woven cloth 5 with the resin by impregnatingthe resin into the nonwoven fabric 5 or the woven cloth 5 inconsideration of the following conditions. Namely, the thermosettingresin layer 3′ in an absolutely liquid state is produced by applyingonto the surface of the copper foil, and hence the resin layer generallycontains a large amount of solvent; thus, when the nonwoven fabric 5 orthe woven cloth 5 is superposed on the surface of the resin layerabsolutely without removing the solvent and is subjected to thefollowing processes, bubbles tend to be generated in the thermosettingresin layer 3′ interposed between the copper foil 2 and the nonwovenfabric 5 or the woven cloth 5 during finally transforming to asemi-cured state. Accordingly, it is preferable to remove a certainamount of solvent, so that the bubble generation can be prevented,before the superposition of the nonwoven fabric 5 or the woven cloth 5on the surface of the thermosetting resin layer 3′. The solvent may beremoved either simply by air drying, or by heating within thetemperature range not exceeding the curing temperature. The solventremoving level can be optionally adjusted in consideration of thethickness of the thermosetting resin layer 3′ and the thickness of thenonwoven fabric 5 or the woven cloth 5 so that the bubble generation canbe suppressed.

[0034] The removal of the solvent from the resin component in thethermosetting resin layer 3′, before the nonwoven fabric 5 or the wovencloth 5 is superposed, is nothing else that the so-called semi-curedstate is formed. In such a case, it is necessary that the resin in thesemi-cured thermosetting resin layer 3′ is impregnated into the nonwovenfabric 5 or the woven cloth 5 under favor of the capillary phenomenonexhibited by any fiber of the glass fiber, the aramid fiber, and thewholly aromatic polyester fiber constituting the nonwoven fabric 5 orthe woven cloth 5 so as to exude from the side surface of the nonwovenfabric or the woven cloth 5 reverse to the surface thereof in contactwith the thermosetting resin layer 3′. Thus, in such a case, the heatingis made at a temperature not exceeding the curing temperature tofluidize again the thermosetting resin layer 3′.

[0035] The thermosetting resin layer 3′ as referred to in the presentmethod is preferably X-30 (μm) to X-3 (μm) in thickness in relation tothe thickness (X (μm)) of the formed insulating layer. For example, whenthe thickness of the insulating layer is made to be 100 μm, the liquidresin is applied onto the surface of the copper foil with the thicknessof the thermosetting resin layer 3′ in the range from 100−30=70 μm to100−3=97 μm. In this way, it becomes possible to form the insulatinglayer with the aimed thickness on the surface of the copper foil 2. Whenthe thickness of the thermosetting resin layer 3′ is made to be lessthan X-30 (μm), the final adhesion between the insulating layer and thecopper foil layer cannot be sufficiently high, while when the thicknessof the thermosetting layer 3′ is made to exceed X-3 (μm), there occursalso no augmenting effect of improving the adhesion between theinsulating layer and the copper foil layer. Incidentally, the thicknessas referred to here means the above described thickness as converted tothe value on the flat plane.

[0036] Among others, as for the copper foil, the nonwoven fabric or thewoven cloth, and the thermosetting resin layer, and the like, thepresent method is the same as the aforementioned method, and the samematerials and the same conditions can be adopted. Accordingly, here areavoided the duplicate descriptions.

[0037] The copper foil with an insulating layer obtained by use of theabove described method is suitably used for the usual printed circuitboards, materials for the printed circuit boards for use in capacitorlayer formation, and the like (in the present specification, all theseboards and materials are generically referred to as “printed circuitboards”), and can maintain the quality of the printed circuit boardswith a satisfactory balance owing to the above described effects.

BEST MODE FOR CARRYING OUT THE INVENTION

[0038] More detailed description will be made below on the presentinvention with reference to the Examples of production of the copperfoils with an insulating layer related to the present invention.

EXAMPLE 1

[0039] In the present Example, according to the flow of production shownin FIG. 2, a copper foil with an insulating layer 1 was fabricated usingan electrodeposited copper foil 2 which had a nominal thickness of 18 μmand a surface roughness (Rz) of 3.5 μm for the roughened surface 4 onwhich the first thermosetting resin layer 3 was formed.

[0040] At the beginning, an epoxy resin composition was prepared whichwas used for forming the first thermosetting resin layer 3 and thesecond thermosetting resin layer 7; bisphenol-A type epoxy resin (brandname: YD-128, Toto Kasei Co., Ltd.) (30 wt %), o-cresol type epoxy resin(brand name: ESCN-195XL80, Sumitomo Chemical Co., Ltd.) (50 wt %), bothas resins, dicyandiamide as an epoxy resin curing agent in the form of adimethylforamide solution with 25% solid content (4 wt % asdicyandiamide) (16 wt %), and 2-ethyl-4-methylimidazole as a curingaccelerator (brand name: Cazole 2E4MZ, Shikoku Corp.) (0.1 wt %) weredissolved in a mixed solvent composed of methyl ethyl ketone anddimethylformamide (mixing ratio: methyl ethyl ketone/dimethylformamide=4/6) to obtain an epoxy resin composition containing a solidcontent of 60%.

[0041] The epoxy resin composition was applied uniformly onto theroughened surface 4 of the electrodeposited copper foil 2 of 18 μm innominal thickness, and the thus treated copper foil was allowed to standat room temperature for 30 minutes; a certain amount of solvent wasremoved by blasting hot air at 150° C. for 2 minutes with a hot airdryer, and the first thermosetting resin layer 3 was dried into asemi-cured state. In this case, the applied amount of the epoxycomposition was so adjusted that the resin thickness became 40 μm afterdrying.

[0042] Then, a nonwoven fabric 5 made of an aramid fiber of 50 μm innominal thickness was attached onto the first thermosetting resin layer3. This attachment was performed in such a way that the nonwoven fabric5 was superposed on the surface of the formed first thermosetting resinlayer 3, and the thus treated copper foil was made to pass through theheat roll 6 heated to 150° C. with the applied lamination pressure of 9kg/cm² in a delivery rate of 20 cm/minute. Consequently, the totalaverage thickness of the first thermosetting resin layer 3 and thenonwoven fabric 5 in an attached state was 55 μm.

[0043] On completion of the attachment of the nonwoven fabric 5, thenthe second thermosetting resin layer 7 was formed. The epoxy resincomposition used for forming the second thermosetting resin layer 7 wasthe same as that used for forming the first thermosetting resin layer 3.Accordingly, description on the epoxy resin composition is omitted hereto avoid a duplicate description.

[0044] The epoxy resin composition was uniformly applied onto theattached nonwoven fabric 5, and the thus treated copper foil was allowedto stand at room temperature for 30 minutes; a certain amount of solventwas removed by blasting hot air at 150° C. for 3 minutes with a hot airdryer, and the second thermosetting resin layer 7 was dried into asemi-cured state. In this case, the applied amount of the epoxy resincomposition was so adjusted that the total thickness of the firstthermosetting resin layer 3, nonwoven fabric 5, and second thermosettingresin layer 7 after drying became 75 μm. As above, the copper foil withan insulating layer 1 was fabricated by use of the manufacturing methodrelated to the present invention.

[0045] According to the flow of production illustrated in FIG. 4, usingthe copper foil with an insulating layer 1 and an inner layer corecomponent 8 (made of an FR-4 material; the board thickness 0.6 mm, thecopper foil thickness 35 μm) with inner layer circuits 9 on the surfacesthereof, a multilayer copper clad laminate 10 for use in performanceevaluation was fabricated; as FIG. 4(1) shows, the inner layer corecomponent 8 as a central component, and two sheets of the copper foilwith an insulating layer 1, with one sheet on each of the two sidesurfaces of the core component 8, were laminated with the insulatinglayer of each copper foil 1 in contact with one of the outer surfaces ofthe core component 8, and were subjected to the press working tofabricate the multilayer copper clad laminate 10. In this case, thepress working conditions were that the press temperature was 180° C.,the press pressure was 20 kg/cm², and the curing time was 90 minutes.

[0046] Furthermore, according to the flow of production illustrated inFIG. 5, an insulating resin board 11 for use in evaluation to be usedfor performance evaluation was fabricated. As FIG. 5(1) shows, twosheets of copper foil with an insulating layer were laminated with theinsulating layers superposed with each other, and were attached to eachother under the press working conditions that the press temperature was180° C., the press pressure was 20 kg/cm², and the curing time was 90minutes, to obtain the first double-sided copper clad laminate 12 asFIG. 5(2) shows. Then, the copper foils on the two side surfaces of thefirst double-sided copper clad laminate were removed by etching to yielda resin board 13 as FIG. 5(3) shows. Then, as FIG. 5(4) shows, twosheets of copper foil with an insulating layer 1 were laminated on theresin board 13 with one sheet to each side surface of the resin board 13and with the insulating layer of each copper foil with an insulatinglayer 1 in contact with one of the outer layer surfaces of the resinboard 13, and were attached to each other under the press workingconditions that the press temperature was 180° C., the press pressurewas 20 kg/cm², and the curing time was 90 minutes, to obtain the seconddouble-sided copper clad laminate 14. The copper foils on the both sidesurfaces of the laminate 14 were removed by etching to fabricate aninsulating resin board 11 for use in evaluation as FIG. 5(6) shows.

[0047] The performance evaluation results for the multilayer copper cladlaminate 10 and the insulating resin board 11 for use in evaluation arecollected in Table 1 so that comparison is possible with the ComparativeExamples to be described below.

EXAMPLE 2

[0048] In the present Example, a copper foil with an insulating layer 1was fabricated according to the flow of production conceptually shown inFIG. 3 by using an electrodeposited copper foil 2 which had a nominalthickness of 18 μm and a surface roughness (Rz) of 3.5 μm for theroughened surface 4 on which the thermosetting resin layer 3′ wasformed.

[0049] The epoxy resin composition used for forming the thermosettingresin layer 3′ was the same as that used in Example 1. Accordingly, hereis made no description on the epoxy resin composition to avoid aduplicate description.

[0050] The epoxy resin composition was applied uniformly onto theroughened surface 4 of the electrodeposited copper foil 2 of 18 μm innominal thickness, and the thus treated copper foil was allowed to standat room temperature for 30 minutes; a certain amount of solvent wasremoved by blasting hot air at 150° C. for 2 minutes with a hot airdryer, and the first thermosetting resin layer 3 was dried into asemi-cured state to result in the resin thickness of 80 μm.

[0051] Then, a nonwoven fabric 5 made of an aramid fiber of 50 μm innominal thickness was attached onto the semi-cured thermosetting resinlayer 3′. This attachment was performed in such a loose way that thenonwoven fabric 5 was superposed on the surface of the formed firstthermosetting resin layer 3′, and the thus treated copper foil was madeto pass through the heat roll 6 heated to 100° C. with the appliedlamination pressure of 5 kg/cm² in a delivery rate of 50 cm/minute.Consequently, the total average thickness of the nonwoven fabric 5 andthe thermosetting resin layer 3′ was 110 μm; neither resin exudationfrom the surface of the nonwoven fabric 5 nor the resin transfer to theheat roll 6 occurred.

[0052] On completion of the attachment of the nonwoven fabric 5 asdescribed above, the thermosetting resin layer 3′ was fluidized again bymaintaining an atmosphere of 150° C. for 1 minute with a hot air dryer,the resin component constituting the thermosetting resin layer 3′ wasimpregnated into the nonwoven fabric 5 under favor of the capillaryphenomenon exhibited by the aramid fiber constituting the nonwovenfabric 5 so as to exude from the side surface of the nonwoven fabricreverse to the surface thereof in contact with the thermosetting resinlayer 3′, and thus the surface of the nonwoven fabric 5 was completelycoated with the resin to yield a copper foil with an insulating layer asshown in FIG. 3(4). In this case, the total thickness of thethermosetting resin layer 3′ and the nonwoven fabric 5 was 90 μm afterdrying.

[0053] A multilayer copper clad laminate 10 was fabricated according tothe method illustrated in FIG. 4 similar to that in Example 1, while aninsulating resin board 11 for use in evaluation to be used inperformance evaluation was fabricated according to the flow ofproduction illustrated in FIG. 5, and the performance evaluation similarto that in Example 1 was performed. The performance evaluation resultsfor the multilayer copper clad laminate 10 and the insulating resinboard 11 for use in evaluation, fabricated as described above, arecollected in Table 1 so that comparison is possible with the ComparativeExamples to be described below.

EXAMPLE 3

[0054] In the present Example, according to the flow of production shownin FIG. 2, a copper foil with an insulating layer 1 was fabricated withthe same method as that in Example 1, except that, contrary to thenonwoven fabric used as a skeletal component in Example 1, a woven clothof 20 μm in thickness was used as a skeletal component which cloth wasan SP glass cloth made of the above described flattened thread andexcellent in the laser drilling workability. Incidentally, the samereference numeral is to be used for the SP glass cloth as that for thenonwoven fabric.

[0055] Now, the matters different form those in Example 1 are describedbelow. The epoxy resin composition was uniformly applied onto theroughened surface 4 of the electrodeposited copper foil of 18 μm innominal thickness, and the thus treated copper foil was allowed to standat room temperature for 30 minutes; a certain amount of solvent wasremoved by blasting the hot air at 150° C. for 2 minutes with a hot airdryer, and the first thermosetting resin layer 3 was dried into asemi-cured state. The applied amount of the epoxy resin composition wasso adjusted that the resin layer thickness was 15 μm after drying.

[0056] Then, the SP glass cloth 5 of 20 μm in nominal thickness wasattached onto the first thermosetting resin layer 3. This attachment wasperformed in such a way that the SP glass cloth 5 was superposed on thesurface of the formed first thermosetting resin layer 3, and the thustreated copper foil was made to pass through the heat roll 6 heated to150° C. with the applied lamination pressure of 9 kg/cm² in a deliveryrate of 20 cm/minute. Consequently, the total average thickness of thefirst thermosetting resin layer 3 and the SP glass cloth 5 in anattached state was 32 μm.

[0057] On completion of the attachment of the SP glass cloth 5,successively the second thermosetting resin layer 7 was formed. Theepoxy resin composition used for forming the second thermosetting resinlayer 7 was the same as that used for forming the first thermosettingresin layer 3. Accordingly, here is omitted the description on the epoxyresin composition in order to avoid a duplicate description.

[0058] The epoxy resin composition was uniformly applied onto theattached SP glass cloth 5, and the thus treated copper foil was allowedto stand at room temperature for 30 minutes; a certain amount of solventwas removed by blasting the hot air at 150° C. for 3 minutes with a hotair dryer, and the second thermosetting resin layer 7 was dried into asemi-cured state. In this case, the applied amount of the epoxy resincomposition was so adjusted that the total thickness of the firstthermosetting resin layer 3, the SP glass cloth 5, and the dried secondthermosetting resin layer 7 was 40 μm. As above, the copper foil with aninsulating layer 1 was fabricated by using the manufacturing methodrelated to the present invention.

[0059] In addition, according to the flow of production illustrated inFIG. 4, an insulating resin board 11 for use in evaluation shown in FIG.5(6) was fabricated on the basis of the method similar to that inExample 1.

[0060] The performance evaluation results for the multilayer copper cladlaminate 10 and the insulating resin board 11 for use in evaluation,fabricated as described above, are collected in Table 1 so thatcomparison is possible with the Comparative Examples to be describedbelow.

EXAMPLE 4

[0061] In the present Example, according to the flow of productionconceptually shown in FIG. 3, a copper foil with an insulating layer 1was fabricated with the same method as that in Example 2, except that,contrary to the nonwoven fabric used as a skeletal component in Example1, a woven cloth of 20 μm in thickness was used as a skeletal componentwhich cloth was an SP glass cloth made of the above described flattenedthread and excellent in the laser drilling workability. Incidentally,the same reference numeral is to be used for the SP glass cloth as thatfor the nonwoven fabric.

[0062] Now, the matters different form those in Example 2 are describedbelow. The epoxy resin composition was uniformly applied onto theroughened surface 4 of the electrodeposited copper foil 2 of 18 μm innominal thickness, and the thus treated copper foil was allowed to standat room temperature for 30 minutes; a certain amount of solvent wasremoved by blasting the hot air at 150° C. for 2 minutes with a hot airdryer, and the first thermosetting resin layer 3 was dried into asemi-cured state to have a thickness of 36 μm.

[0063] Then, an SP gals cloth 5 of 20 μm in nominal thickness wasattached onto the semi-cured thermosetting resin layer 3′. Thisattachment was performed in such a loose way that the SP glass cloth 5was superposed on the surface of the formed thermosetting resin layer3′, and the thus treated copper foil was made to pass through the heatroll 6 heated to 100° C. with the applied lamination pressure of 5kg/cm² in a delivery rate of 50 cm/minute. Consequently, the totalthickness of the SP glass cloth 5 and the thermosetting resin layer 3′was 56 μm. Neither resin exudation from the surface of the SP glasscloth 5 nor resin transfer to the heat roll 6 occurred.

[0064] On completion of the attachment of the SP glass cloth 5 asdescribed above, the thermosetting resin layer 3′ was fluidized again bymaintaining in a atmosphere of 150° C. for 1 minute by using a hot airdryer, and the resin component constituting the thermosetting resinlayer 3′ was impregnated into the SP glass cloth under favor of thecapillary phenomenon exhibited by the fiber constituting the SP glasscloth 5, so as to exude from the side surface of the SP glass cloth 5reverse to the surface thereof in contact with the thermosetting resinlayer 3′, and thus the surface of the SP glass cloth 5 was completelycoated with the resin to yield a copper foil with an insulating layer asshown in FIG. 3(4). In this case, the total thickness of thethermosetting resin layer 3′ and the SP glass cloth 5 was 42 μm.

[0065] Then, a multilayer copper clad laminate 10 was fabricatedaccording to the method shown in FIG. 4 similar to that in Example 1,while an insulating resin board 11 for use in evaluation to be used inperformance evaluation was fabricated according to the flow ofproduction shown in FIG. 5, and the performance evaluation similar tothat in Example 1 was performed. The performance evaluation resultsobtained for the multilayer copper clad laminate 10 and the insulatingresin board 11 for use in evaluation, fabricated as described above, arecollected in Table 1 so that comparison is possible with the ComparativeExamples to be described below.

COMPARATIVE EXAMPLE 1

[0066] In the present Comparative Example, the same resin composition asused in Example 1 was uniformly applied onto the roughened surface of anelectrodeposited copper foil of 18 μm in nominal thickness, and the thustreated copper foil was allowed to stand at room temperature for 30minutes; a certain amount of solvent was removed by blasting the hot airat 150° C. for 5 minutes with a hot air dryer, and the resin layer wasdried into a semi-cured state to yield a copper foil containing noconventional skeletal component. In this case, the applied amount of theepoxy resin composition was so adjusted that the thickness of the resinlayer was 75 μm after drying.

[0067] By using the copper foil with resin in place of the copper foilswith an insulating layer 1 used in Examples described above, amultilayer copper clad laminate and an insulating resin board werefabricated according to the methods similar to those in Example 1, andwere subjected to the performance evaluation. The performance evaluationresults are shown in Table 1 to be described below in comparison withthe results of Examples.

COMPARATIVE EXAMPLE 2

[0068] An epoxy resin composition was newly prepared by adding methylethyl ketone to the epoxy resin composition in such a way that the solidcontent of the newly prepared composition was 50%. The newly preparedcomposition was impregnated into a glass cloth (a conventional wovencloth for use in FR-4 without improvement for the laser drillingworkability) of 60 μm in thickness. The impregnated glass cloth wasallowed to stand at room temperature for 30 minutes, and a certainamount of solvent was removed by blasting the hot air at 150° C. for 5minutes to prepare a prepreg. The thickness of the prepreg was made tobe 75 μm after drying.

[0069] A multilayer copper clad laminate was fabricated by using theprepreg obtained and by attaching the electrodeposited copper foil of 18μm in thickness onto the outer layers of the inner layer core componentused in Examples. The multilayer copper clad was a multilayer printedcircuit board which had a layer structure similar to those in Examples,and in which the inner core component occupies the central portion, theprepreg was superposed onto both outer layers of the inner layer corecomponent, and a copper foil of 18 μm in thickness was laminated ontothe outer surface of each prepreg layer. The press conditions for thiscase was similar to those in Examples, so that description is omitted onthe conditions to avoid a duplicate description.

[0070] A resin board for use in evaluation was fabricated in such a waythat 4 sheets of prepreg were laminated and interposed between the twosheets of mold-releasing paper, and subjected to press working under theconditions that the press temperature was 180° C., the press pressurewas 20 kg/cm², and the curing time was 90 minutes. The multilayer copperclad laminate and insulating resin board for use in evaluationfabricated as described above were subjected to the performanceevaluation. The evaluation results obtained are shown in Table 1 to bedescribed below in comparison with Examples.

[0071] Evaluation Methods and Evaluation Results

[0072] Description will be made on the evaluation methods related to themultilayer copper clad laminates and insulating resin boards for use inevaluation fabricated in the above described Examples and ComparativeExamples. As for the multilayer copper clad laminates, the followingitems (1) to (4) were evaluated.

[0073] (1) Evaluation of the embedding property of the inner layercomponent

[0074] This evaluation is concerned with investigation as to whether thevoids were generated in the inner layer circuit cans on attachment ontothe inner layer component. No void generation is indicated by the symbol“O” and a void generation by the symbol “X”.

[0075] (2) Evaluation of solder heat standing property According to amethod in compliance with JIS C 6481, a fragment of a board was dippedinto a solder bath at 260° C. and the measurement was made on the timeelapsed until swelling occurs.

[0076] (3) Evaluation of copper foil peel strength In compliance withJIS C 6481, a circuit of 0.2 mm in width was formed by etching and thepeel strength was measured.

[0077] (4) Evaluation of laser drilling workability The time required todrill 1000 via holes of 100 μm in diameter by use of a carbon dioxidelaser drilling machine was measured and the shape characteristics suchas drilled hole diameters were inspected. In this case, the irradiationconditions of the carbon dioxide laser were that the frequency was 2000Hz, the mask diameter was 5.0 mm, the pulse width was 60 gsec, the pulseenergy was 16.0 mJ, the offset was 0.8, the laser light diameter was 130μm, and the hole diameter intended to form was 100 μm.

[0078] Now, description will be made below on the evaluation itemsapplied to the insulating resin boards for use in evaluation. Theevaluation items for the insulating resin board are the following twoitems I) and II) mainly concerned with the strength as the insulatingresin board.

[0079] I) Evaluation of Bending Strength

[0080] The bending strengths of the insulating resin boards for use inevaluation were measured in compliance with JIS K 7171.

[0081] II) Evaluation of Thermal Expansion Coefficient

[0082] The thermal expansion coefficients of the insulating resin boardsfor use in evaluation were measured in compliance with a test methoddescribed in the paragraph 2.4.24.5 in IPC-TM-650 which specifies thetest method of IPC standard. TABLE 1 Comparative Comparative Evaluationitem Unit Example 1 Example 2 Example 3 Example 4 example 1 example 2Embedding — ◯ ◯ ◯ property of inner layer component Solder heat standingsec Equal to or larger than 600 Equal to or Equal to or property largerthan 600 larger than 600 Copper foil peel Kgf/cm 1.2 1.2 1.2 strengthLaser Time sec 120 125 90 180 drilling Shape ◯ ◯ X workability Bendingstrength MPa 280 420 95 550 Thermal expansion ppm/° C. 15 10 60 20coefficient

[0083] Table 1 collects the evaluation results concerned with the itemsdescribed above. The following facts are revealed from Table 1. First ofall, a comparison between Examples reveals that the evaluation resultsof Example 1 and those of Example 2 are the same, while the evaluationresults of Example 3 and those of Example 4 are the same. In otherwords, there occurs a large difference in a mechanical strength of thebending strength depending on the type of the skeletal component. Asexpected, the laser drilling workability seems to be somewhat better inthe cases where a nonwoven fabric was used as the skeletal component.The thermal expansion coefficient has been found to be smaller in thecases where an SP glass cloth was used as the skeletal component.

[0084] From comparison between Examples and Comparative Examples, it hasbeen found that the use of the copper foils with an insulating layer ofExamples can deduce comparable performances with those deduced by use ofthe copper foils with an insulating layer of Comparative Examples, withrespect to the three items among the evaluation items for the multilayercopper clad laminate, that is, the evaluation of the inner layerembedding property, the evaluation of the solder heat standing property,and the evaluation of the copper foil peel strength. However, there aredifferences among Examples and Comparative Examples regarding theevaluation of the laser drilling workability. As is anticipated, thecase most excellent in the laser drilling workability is the one wherewas used the copper foil with resin of Comparative Example 1 which didnot contain such a skeletal component as a nonwoven fabric or a wovencloth. On the other hand, the case poorest in the laser drillingworkability, in the sense that a long time was required for holedrilling and the stability in drilled hole shape was poor, is the caseof Comparative Example 2 where was used the FR-4 base materialcontaining a conventional glass cloth in the interior thereof. Thus, thelaser drilling workability of the multilayer copper clad laminate whichused the copper foil with an insulating layer related to the presentinvention is found to lie midway between that evaluated in ComparativeExample 1 and that evaluated in Comparative Example 2.

[0085] Turning to the evaluation results for the insulating resinboards, the bending strengths evaluated in Examples related to thepresent invention are found to lie midway between that evaluated inComparative Example 1 and that evaluated in Comparative Example 2. To bemore specific, the insulating resin boards of Examples are inferior instrength to that containing FR-4 therein, but exhibit strengthsincreased by a factor of 2.5 or above as compared to that of theinsulating board in Comparative Example 1 which used a conventionalcopper foil with resin known to have an insufficient strength; thebending strengths of the insulating resin boards of Examples are foundto be increased drastically so that the risk of board cracking isdiminished to a large extent. Particularly, the bending strengthsevaluated in Examples 3 and 4 where an SP glass cloth was used are foundto approach closer to that evaluated in Comparative Example 2.

[0086] As for the thermal expansion coefficients of the insulating resinboards for use in evaluation, the thermal expansion coefficientsevaluated in Examples are smaller than those evaluated in ComparativeExamples 1 and 2, and hence the insulating resin boards of Examples areregarded as excellent in the board dimensional stability. Taking thematerials constituting the insulating layer as the resin and skeletalcomponent, it is the resin that has the possibility of generating thelargest thermal expansion. Accordingly, it seems natural that thethermal expansion coefficient evaluated in Comparative Example 1 where acopper foil with resin containing no skeletal component is largest. Onthe other hand, as compared to the insulating resin board of ComparativeExample 2 which contain a conventional glass cloth as a skeletalcomponent, the smaller thermal expansion coefficients have been found ineither the insulating resin boards of Examples 1 and 2 which contain anowoven fabric of aramid fiber or the insulating resin boards ofExamples 3 and 4 which contain an SP glass cloth with a smaller numberof glass cloth fibers in a strand.

[0087] Industrial Applicability

[0088] As can be seen fro the above, the copper clad laminate fabricatedby use of the copper foil with an insulating layer produced by themanufacturing method related to the present invention has a strength alittle lower than that found for the case where the FR-4 base materialis used, but carries on an excellent laser drilling workability,provides an excellent dimensional stability to the board through holdinga small thermal expansion coefficient, and can prevent the boardcracking through acquiring a strength in a degree free of problem fromthe standpoints of the conventional fabrication process of a copper cladlaminate to make a printed circuit board, the loading weight to beapplied when incorporated into electronic appliances, and such externalloads as vibration. Thus, an excellent and high degree of qualitystability can be achieved, as compared with the case where a copper foilwith resin is used.

1. A method of manufacturing a copper foil provided with a semi-curedinsulating layer containing a skeletal component on one side surface ofthe copper foil which method is a method of manufacturing a copper foilwith an insulating layer, wherein the first semi-cured thermosettingresin layer is provided with on one side surface of the copper foil; anonwoven fabric or a woven cloth to be the skeletal component ispress-bonded onto said first thermosetting resin layer; the secondthermosetting resin layer is formed on the surface of said press-bondednonwoven fabric or woven cloth; and a semi-cured insulating layer whichcontains a nonwoven fabric or a woven cloth on one side surface of thecopper foil is formed by drying into a semi-cured state.
 2. The methodof manufacturing a copper foil with an insulating layer according toclaim 1, wherein the thickness of the first thermosetting resin layer is5 μm or above as converted to a flat plane thickness, and thinner thanthe thickness of the nonwoven fabric or the woven cloth used as theskeletal component.
 3. A method of manufacturing a copper foil providedwith a semi-cured insulating layer containing a skeletal component onone side surface of the copper foil which method is a method ofmanufacturing a copper foil with an insulating layer, wherein a liquidthermosetting resin layer is provided on one side surface of the copperfoil; a nonwoven fabric or a woven cloth to be the skeletal component issuperposed onto said thermosetting resin layer; the resin constitutingsaid thermosetting resin layer is impregnated into said nonwoven fabricor woven cloth so as to exude form the reverse side surface so that saidnonwoven fabric or woven cloth is coated with the resin constituting thethermosetting resin; and a semi-cured insulating layer which contains anonwoven fabric or a woven cloth on one side surface of the copper foilis formed by drying into a semi-cured state.
 4. The method ofmanufacturing a copper foil with an insulating layer according to claim3, wherein the thermosetting resin layer has the thickness in the rangefrom X-30 (μm) to X-3 (μm) in relation to the thickness of the formedinsulating layer (X (μm)).
 5. The method of manufacturing a copper foilwith an insulating layer according to claim 1, wherein the nonwovenfabric or the woven cloth is made of any of a glass fiber, an aramidfiber, or a wholly aromatic polyester fiber having a melting point of300° C. or above.
 6. A copper foil with an insulating layer fabricatedby the manufacturing methods according claim
 1. 7. A printed circuitboard obtained by use of the copper foil with an insulating layeraccording to claim 6.